The present invention relates to a miniature pump assembly, particularly to a miniature dual syringe-type pump assembly, and more particularly to a miniature dual syringe-type pump assembly for supplying new and withdrawing used reagent from a reagent sensor, for example.
Ground water contamination by various chemicals, such as trichloroethylene (TCE), carbon tetrachloride, and chloroform, for example, has become a major concern. The potential health problems arising from chronic exposure and/or ingestion of various carcinogenic chlorinated solvents, such as TCE, as a major U.S. health concern. Such compounds have been inadvertently or unknowingly introduced into the environment over many years through commercial, government, and private activities, such as by vehicle or aircraft fueling, and maintenance facilities, dumping of various chemicals, etc. These contaminants over time seep into the underground water supply, thereby resulting in latent health problems. The remediation of this potential problem is a current major focus by federal and state agencies.
One of the major costs of ground water investigations and cleanup is chemical analyses, and substantial effort has recently been directed to developing sensors that will enable researches and remediators the ability to detect, measure, and monitor the presence of various contaminants. Early efforts involved drilling and sampling technologies which resulted in cross contamination of dirty and clean zones and thus the data retrieved was questionable. At the Lawrence Livermore National Laboratory (LLNL), for example, efforts have been directed for many years toward the development of chemical detectors or sensors, and more recently for developing and field testing fiber-optic-based optical sensor systems for quantitative analysis of contaminants, such as TCE, carbon tetrachloride, and chloroform. The objectives of the LLNL program are to: 1) modify existing optical sensor technology for continuous in situ monitoring of specific contaminants, 2) develop viable downhole sensor placement technologies, 3) extend the technology to the measurement of other contaminants, and 4) deliver the technology in a device capable of using in the field.
The optical sensor system is based upon the fact that certain reagents produce a fluorescence or colored products in the presence of small amounts of volatile organic compounds (VOCs). For example, a fluorescence-based probe for chloroform, was developed at LLNL in the mid-1980's, in which the sensor irradiated a reagent with filtered light causing a fluorescence that could then be measured, with the degree of fluorescence being proportional to the concentration of the contaminant. However, this sensor did not have the desired sensitivity or reliability. In the later 1980's a new sensor concept was developed at LLNL based on the absorption of light by the reagent color change.
Based on the reagent color change approach, a chemical contamination measurement system has been developed. See "Fiber Optic Sensor for Continuous Monitoring of Chlorinated Solvents in the Vadose Zone and in Groundwater": Field Test Results, SPIE, Vol. 1587 Chemical, Biochemical, and Environmental Fiber Sensors 111 (1991), pg. 279-282, published Feb. 24, 1992; and UCRL-JC-110528, "Innovative Characterization Techniques and Decision Support Systems For Ground Water Contamination Projects", F. Hoffman, July 1992. The basic components of this measurement system are: 1) a sensor, 2) a pumping system or renewing the chemical reagent in the sensor, which includes a computer controlled pump and six-way valve, and 3) an electro-optical readout device also attached to the computer, including an incandescent lamp, suitable filters and silicon diode detectors, for measuring sensor transmission. The sensor allows consecutive measurements to be taken at short intervals on an on-demand basis, with control and monitoring being executed remotely under software control.
When the sensor of the above-referenced measurement system (SPIE Vol. 1587 and UCRL-JC-110528) is placed in the proximity of the head space of a water stream or in a vapor stream containing the contaminant, the contaminant diffuses through a membrane on the sensor, contacts the reagent therein, and produces a colored product. The sensor includes two optical fibers, one of the fibers carrying the incident light, and the other transmitting the light reflected off the membrane back to the sensor readout. In the case of the contaminant being TCE, two wavelengths of light are of interest: 540-nanometer (nm) light is absorbed by the color change in the reagent; 640 nm light is also examined because the colored products are transparent to that wavelength and provides an internal standard. The ratio of 540 to 640 nm light at the sensor readout device provides a noise-free measure of 540 nm absorption.
When the analysis begins, the computer attached to the control center of the system monitors the rate of change of absorption, which is proportional to the concentration of the contaminant in the sample. The sensor is also equipped with reagent supply or source and reagent waste tubes connected to the pumping system, which is controlled to renew the reagent in the sensor. When the analysis is complete, the computer controls the injection of new reagent into the sensor and evacuates the old, colored reagent.
One of the critical components of the above-referenced measurement system is the pump assembly which enables reagent supply to and removal from the sensor. This requirement is compounded by the small size requirement, such as in a well packer assembly or in a cone penetrometer, which is adapted to be driven into the ground. Small-size precision metering pumps are known in the art are exemplified U.S. Pat. No. 4,752,192 issued Jun. 21, 1988 to B. Ode, and U.S. Pat. No. 4,915,591 issued Apr. 10, 1990 to H. Funke. While these prior known miniaturized pumps provide certain capabilities, a need existed for a pump arrangement capable of being located in a small diameter tube or component and being remotely controlled for simultaneous and consistent supply and removal of a material to and from a chamber, such that there is no intermixing at the new and old material. The present invention satisfies this need by providing a pumping arrangement which utilizes a pair of syringe-type pumps actuated by a control mechanism which provides simultaneous pushing on one syringe and pulling on the other.